This invention relates to a method of injection molding about the surface of an object, and in particular to a two stage method that helps to ensure an approximately even coverage of injection molded material about the object.
Injection molding is a commonly used method of manufacturing a large number of different parts and devices made from plastic, nylon or other injection moldable materials. Injection molded products are typically manufactured quickly and at a relatively low cost, and often result in a finished product with a smooth, non-abrasive and corrosion resistant finish. Various different surface configurations are also readily formed through injection molding. Unfortunately, a significant limitation of injection molded products is their tendency to exhibit a low inherent tensile and compressive strength. Typically injection molded products formed from plastic, nylons or other materials have significantly lower tensile and compressive strengths than similar products made from metal.
In order to create a product having many of the benefits and attractiveness of an injection molded product, but at the same time having the inherent strength of a metallic product, others have made attempts to injection mold over metallic and similar objects. Unfortunately, existing molding techniques have proven to be somewhat less than ideal with the finished product often having an uneven coating of injection molded material about its outer surface. Such difficulty most often stems from the inability to accurately hold an object within a mold cavity prior to injection molding so as to ensure even coverage. With an injection molded covering material unevenly dispersed over the surface of the object, there exists the potential for the covering to more readily become detached thereby exposing the underlying metal or other substrate. Such an event can lead to premature wear of the underlying object and corrosion problems. In cases where the injection molding covering is used for electrical insulation, a loss or thinning of the covering can result in the product becoming conductive, and potentially dangerous.
The invention therefore provides a method of injection molding around the surface of an object that addresses a number of the limitations of pre-existing methods currently in use. In particular, in one preferred embodiment the method according to the present invention provides a means to injection mold material about the surface of an object through a two-stage process that helps to ensure a substantially even coverage of material about the surface of the object.
Accordingly, in one of its aspects the invention provides a method of injection molding material around the surface of an object, the method comprising the steps of: positioning the object within the cavity of a first mold, said object held within said mold cavity through the use of a plurality of clamping mechanisms that contact the surface of said object; injection molding material about the surface of said object, said material encompassing the surface of said object except for the points of contact between said clamping mechanisms and said object, said step of injection molding material about the surface of said object including the formation of a plurality of protrusions extending outwardly from the surface of said object, said protrusions formed of said injection molded material; allowing said injection molded material to at least partially solidify about the surface of said object; removing said object with said injection molded material about its surface from said first mold cavity and positioning said object within the cavity of a second mold; securing said object within said second mold cavity through engagement of said plurality of outwardly extending protrusions with the interior surface of said second mold; and injection molding additional material about the surface of said object, said additional material encompassing said object and said at least partially solidified material except for points of contact between said outwardly extending protrusions and the interior surface of said second mold.
Further aspects and advantages of the invention will become apparent from the following description taken together with the accompanying drawings.